st: R-squared between in Xtreg FE

Hi all,
I am still on self-learning of panel data. sorry if my question is too simple.
I know that FE captures only within-variation, so what does the "R-squared
between" indicate?
Actually, in my research, I am not only interested in the hypothesis that x
causes y over history within units, but also the hypothesis that higher x
causes higher y across units (for each given year). Also, i want to get
estimates for time-invariant unit-variant control variables.
So, I may need a meaningful R-squared within. Which model is the best for me?
Thanks.
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/